The invention relates to an installation for the gas-phase polymerisation of at least one olefinic monomer, comprising at least one horizontal stirred reactor, provided with a number of gas feeds in the bottom section of the reactor and a number of liquid feeds in the top section of the reactor and at least two gas outlets at the top of the reactor.
Such a reactor is known from U.S. Pat. No. 3,957,448. The cross-section of this reactor is substantially circular. In the centre of the reactor there is a longitudinal revolving shaft with blades that can stir a polymer bed. The blades preferably bring about no forward or backward transport of the polymer in the polymer bed.
The known reactor is divided into two or more compartments by means of one or more vertical partitions. Each compartment is provided with a number of its own gas feeds at the bottom and a number of its own liquid feeds at the top and a separate gas outlet at the top. This makes it possible to feed to each compartment its own reaction mixture, if desired differing from that in the other compartments, via the gas and the liquid feeds.
Via the liquid feeds at the top of the reactor liquid is fed which as a rule contains one or more components to be reacted, but can also contain inert components as coolant. Suitable inert components in case the reaction components comprise alkenes, are for example propane and higher alkenes. On contact with the polymer bed the liquid evaporates and this ensures that at least part of the heat of reaction released in the polymerisation is removed.
Gas is fed via the gas feeds at the bottom of the reactor. This gas likewise contains one or more components, for example hydrogen, or one or more olefinic monomers and can also contain inert components.
The unreacted olefinic monomers and inert gases from the supplied and evaporated liquid and gas collect at the top of the reactor and are removed from there through the gas outlets at the top of the reactor. The gases from the different compartments are thus removed separately and can also be processed separately and after processing returned to the gas and liquid feeds of the corresponding compartment. This is of great importance because the removed gases from the different compartments can have a different composition. Mixing the removed gases from the different compartments requires extra efforts to separate these again to make suitable flows to be fed to the different compartments.
The vertical partitions in the known reactor extend over the whole cross-section of the reactor in order to prevent exchange of gas between the different compartments. Because each compartment also has its own gas outlet, the desired separation of gas mixtures can take place outside the reactor. Transport of polymer particles from the one compartment to the other is made possible in the known reactor by openings in the partitions. These openings are situated under the surface of the polymer bed. Because the reactor is provided on one side with an outlet for the formed polymer powder a flow is set off in the reactor in the direction of that outlet.
The known installation is suitable to manufacture polymers of a mixed composition, with in a first compartment a polymer being prepared whose composition is determined by the gas composition and the reaction conditions in that first compartment. Via the openings in the partition the formed polymer powder then enters an adjoining, second compartment. If the gas composition or particular reaction conditions in this second compartment differ from those in the first compartment, then the polymer formed in this second compartment will differ in composition or in for example properties such as molecular weight or molecular weight distribution from the polymer formed in the first one. The polymer finally removed from the reactor at the end of the last compartment thus has a mixed composition, for example a bimodal molecular weight distribution, or is in essence a very homogeneous mixture of two or more polymers, each having a different composition.
A disadvantage of the known reactor lies in the fact that the compartments are separated by physical, fixed walls and thus have a fixed size. This seriously limits the scope to choose for example the relative proportions of the polymer components in the mixed compositions.